1. Field of the Invention
This invention relates to new polythiols and their use in curing or hardening polyepoxide resins to produce hard, insoluble, infusible films, castings and adhesives.
2. Description of the Prior Art
Polyglycidyl ethers, particularly those prepared from a dihydric phenol such as Bisphenol A, i.e., 2,2- bis(4-hydroxyphenyl)propane, and an epihalohydrin such as epichlorohydrin, also referred to as epoxy resins, epoxide resins, polyepoxide resins or polyepoxides are important commercial products. When cured, these thermosetting resins form insoluble, infusible films, pottings, castings, adhesives, and the like, and are markedly superior in their physical, chemical, and electrical properties to many other cured thermosetting resins. They exhibit low shrinkage during curing. The combination of hardness and toughness exhibited by the cured resins, their high adhesive strength, resistance to degradation by solvents and other chemicals and their electrical properties, such as dielectric constant and resistivity, are outstanding. At the same time, these properties can be varied within wide limits depending on the end use intended for the resin. Of the wide variety of hardeners, curing agents, or homopolymerization catalysts which have been used to cure polyepoxide resins, no one is suitable for all applications, and many have serious drawbacks no matter what the application.
Among the curing agents for epoxy resins are polythiols, generally used in combination with tertiary amines as catalyst or accelerator. See, for example U.S. Pat. No. 3,258,459 --Le Fave et al, June 28, 1966 describing use of thiol terminated polyoxyalkylene glycols in combination with a tertiary amine accelerator and U.S. Pat. No. 4,177,173 --Carr, Dec. 4, 1979 describing a curing system for polyepoxide resins composed of polymercaptan and poly [(N,N-dimethylamino) alkyl] ethers as catalyst.